There has long been considerable interest in the non-invasive monitoring of body chemistry. There are 16 million Americans with diabetes, all of whom would benefit from a method for non-invasive measurement of blood glucose levels. Using currently accepted methods for measuring blood glucose levels, many diabetics must give blood five to seven times per day to adequately monitor their health status. With a non-invasive blood glucose measurement, closer control could be imposed and the continuing damage, impairment and costs caused by diabetes could be minimized.
Blood oximetry is an example of an application of electronic absorption spectroscopy to non-invasive monitoring of the equilibrium between oxygenated and deoxygenated blood (U.S. Pat. No. 5,615,673, issued Apr. 1, 1997). Similarly, vibrational spectroscopy is a reliable mode of quantitative and qualitative ex vivo analysis for complex mixtures, and there are reports of in vitro applications of this method to metabolically interesting analytes (A. J. Berger et al., 1999, Multicomponent blood analysis by near infrared spectroscopy, Applied Optics 38(13):2916-2926 ; S. Y. Wang et al, 1993, Analysis of metabolites in aqueous solution by using laser Raman spectroscopy, Applied Optics 32(6):925-929; A. J. Berger et al., 1996, Rapid, noninvasive concentration measurements of aqueous biological analytes by near-infrared Raman spectroscopy, Applied Optics 35(1):209-212). Infrared measures, such as vibrational absorption spectroscopy, have been applied to skin tissue, but with success limited by unavailability of suitable light sources and detectors at crucial wavelengths, and by heating of the tissue due to the absorption of incident radiation (U.S. Pat. No. 5,551,422, see also R. R. Anderson and J. A. Parrish, 1981, The Optics of Human Skin, J. Investigative Dermatology 77(1):13-19). Previous attempts to provide methods for noninvasive blood glucose monitoring are summarized in U.S. Pat. No. 5,553,616, issued on Sep. 10, 1996, and in O. S. Khalil, 1999, Spectroscopic and clinical aspects of noninvasive glucose measurement, Clinical Chemistry 45:165-177.
Application of noninvasive techniques for blood analysis will require improved methods for isolating signals attributable to blood versus surrounding tissues.